Modulatory Effects of Exogenously Applied Polyamines on Postharvest Physiology, Antioxidant System and Shelf Life of Fruits: A Review

Abstract

Polyamines (PAs) are natural compounds involved in many growth and developmental processes in plants, and, specifically in fruits, play a vital role regulating its development, ripening and senescence processes. Putrescine (PUT), spermine (SPE), and spermidine (SPD) are prominent PAs applied exogenously to extend shelf life of fruits. They also originate endogenously during developmental phases of horticultural crops and simultaneously affect the quality attributes and shelf life. Their anti-ethylene nature is being exploited to enhance the shelf life when exogenously applied on fruits. In growth and development of fruits, PA levels generally fall, which marks the beginning of senescence at postharvest phase. PUT, SPE and SPD treatments are being applied during postharvest phase to prolong the shelf life. They enhance the shelf life of fruits by reducing respiration rate, ethylene release and enhance firmness and quality attributes in fruits. PAs have a mitigating impact on biotic and abiotic stresses including chilling injury (CI) in tropical and sub-tropical fruits. PAs are environment friendly in nature and are biodegradable without showing any negative effect on environment. Biotechnological interventions by using chimeric gene constructs of PA encoding genes has boosted the research to develop transgenic fruits and vegetables which would possess inherent or in situ mechanism of enhanced biosynthesis of PAs at different stages of development and thereby will enhance the shelf life and quality in fruits. Internal and external quality attributes of fruits are improved by modulation of antioxidant system and by strengthening biophysical morphology of fruits by electrostatic interaction between PAs and phospholipids in the cell wall.

Keywords: S-adenosyl methionine; antioxidants; chilling injury; encoding genes; ethylene; physiology; polyamines; putrescine; respiration; shelf life; spermidine; spermine.

Figure 1

Biosynthetic pathway of three naturally synthesised prominent polyamines: Spd, Spermidine; Spe, Spermine; Pu, Putrescine. Precursors involved in biosynthesis: l-Arginine, l-Ornithine; N-carbamoylputrescine; Agmatine; Methionine; SAM, S-adenosylmethionine; ACC, 1-aminocyclopropane-1-carboxylic acid. Enzymes involved in the pathway: ADC, Arginine decarboxylase; ODC, Ornithine decarboxylase; AIH, Agmatineimino hydrolase; N-CarbamoylputrescineAminohydrolase; SpdS, Spermidine synthase;SpmS, Spermine synthase.

Figure 2

Possible actions of exogenously applied polyamines on fruits and mitigating CI and improving shelf life; PG, Polygalacturanase; SOD, Superoxide dismutase; LOX, Lipoxygenase; PLD, Phospholipase D; Decreasing trend (); Increasing trend ().

Figure 3

Mechanism of Chilling stress causing chilling injury: PLD, Phospholipase D; LOX, Lipoxygenase; ATP, Adenosine triphosphate; ROS, Reactive oxygen species; MDA, Malondialdehyde.

Figure 4

Scheme showing the over expression of transgenes encoding polyamines with suitable promoters for improving quality attributes and shelf life of horticulture crops.